In the water supply, gas supply, chemical industry, etc. . . . use is often made of a ball valve (spherical valve) to open or close pipes. Such a valve will completely or partially close off the flow of a liquid or gas by means of a sealing member in the form of a drilled sphere (ball) which is rotatable about its axis at right angles to the bore. By rotating the ball through 90°, the valve either moves from being open to being closed or vice versa.
Currently, there are two types available on the market. The first type has two separate inner components (sealing member and operating spindle) which are connected to each other via a lock connection and are each provided with a corrosion-resistant fluoropolymer coating layer. This type has the advantage that, in use, the sealing member is always pressed against the seal by means of the medium flowing through the ball valve (floating ball principle) and thus results in a perfect seal. The operating forces which are transmitted via the lock connection are unfortunately passed directly onto the plastic coatings of both components. In the case of intense use, this may result in damage to the plastic coatings, as a result of which the corrosion resistance is no longer guaranteed. Such a ball valve is shown in FIG. 9 of the US patent publication U.S. Pat. No. 3,825,030.
With the other type of ball valve, in which the sealing member and the operating spindle are formed as a single part, there is no risk of damage to the fluoropolymer coating as there is no lock connection. However, such valves have a different drawback, i.e.: if the ball is pushed into the sealing ring (seats) as a result of the internal medium pressure; then this will also lead to a slight displacement of the ball. Since the ball and spindle are formed as a single part, the operating spindle will also be displaced slightly, as a result of which the sealing kit provided in the space between the housing and the operating spindle will be subjected to an eccentric load. In most cases, this will lead to leakage. Such a type of (single-part) ball valve is described, inter alia, in the following patent publications: EP 0 242 927 A1, DE 44 14 716 A1, in FIGS. 1 to 8 of U.S. Pat. No. 3,825,030 A, DE 30 23 230 A1 and WO 03/071172 A1.